Chapter 14. The RS422/485 communication of GM6-CPUB
14-6
14.6 Communication method and termination resistor
1) Data type
Data bit
: 8 bits
Stop bit
: 1 bit
Parity
: None
2) Communication speed (Baud rate) : Selectable one of 9600, 19200, 38400 bps
3) Termination resistor
When use a long cable for connecting two or more PLCs, a termination resistor should be
connected at the both ends of network. Otherwise, the communication can be disturbed by the
reflected wave of cable. The termination resistor should be 1/2W grade and have the equivalent
resistance with the characteristic impedance of cable. (When use the RS-422 protocol, connect
two termination resistors between SDA and SDB, RDA and RDB. With the RS- 485 protocol,
connect a termination resistor between RDA and RDB, or SDA and SDB.)
14.7 RS-422/485 pin assignment
1) The RS-422 network is connected with 5- pin connector. The following table shows the name,
and description of each pins and direction of signal.
Pin No.
MASTER
Signal direction
SLAVE
1
RDA
SDA
2
RDB
SDB
3
SDA
RDA
4
SDB
RDB
5
SG
SG
2) When using RS- 485 interface, connect cable as RS -422 interface, then interconnect RDA and
SDA, RDB and SDB. With the RS-485 interface, the send / receive signals share one line and
communication is performed as half-duplex method.